Such a stone trap assembly for a harvester is for example known from U.S. Pat. No. 3,576,188. FIGS. 1 and 2 of U.S. Pat. No. 3,576,188 show a stone-catching gap 50 between the discharge edge 42 of the feeder portion 41 and the leading edge 33 of the threshing mechanism 32. This stone catching gap thus forms an entrance of the stone trap assembly which allows reception of foreign objects from a crop flow path for accumulation into the stone trap assembly. During a harvesting operation, after an initial phase in which the stone trap assembly gets filled with crop, the crop flow path moves along this entrance from the feeder to the threshing mechanism. Any stones or other foreign objects are propelled, in the example of U.S. Pat. No. 3,576,188 by the threshing drum 31, through the entrance into the stone trap assembly for accumulation. At regular intervals, for example in between two consecutive harvesting operations, the operator of the harvester will perform an evacuation operation in order to remove the accumulated foreign objects from the stone trap assembly. According to the example of US376188, this is done by rotating a door, formed by an elongate plate 64 and elastomeric sheet 66, around a transverse axis 63 from a closed position in which it closes off an exit at the bottom of the stone trap assembly, to an evacuation position shown in dot stripe lines in FIG. 2 of U.S. Pat. No. 3,576,188 in which the door opens up this exit such that accumulated foreign objects can be evacuated during the evacuation operation. As shown, this rotation can be performed manually by means of a suitable handle. As further shown in FIGS. 2 and 3 of U.S. Pat. No. 3,576,188 the stone trap assembly further comprises a transverse rear edge 73 formed by a plurality of bars 71 that, are attached to the pivot shaft 62, for simultaneous rotation around the transverse axis 63 with the door. As shown these bars 71 form an impeller that is movable, simultaneously with the door, between a retracted position when the door is in the closed position as shown in full lines in FIG. 2 of U.S. Pat. No. 3,576,188 and an extended position when the door is in the evacuation position as shown in dot stripe lines in FIG. 2. It is clear that in its retracted position the impeller generally allows accumulation of the foreign objects during the harvesting operation. When the impeller is moved by means of a rotation from its retracted position to its extended position, which is closer towards the exit, the impeller forces the accumulated foreign objects towards the exit of the stone trap assembly during the evacuation operation.
One problem with such a known stone trap assembly is that the impeller forces the crop and foreign objects against the front wall during the evacuation operation, thereby reducing the efficiency of the evacuation operation as there is an increased risk for some of the crop and foreign objects to clog or adhere to the impeller, the door and/or the front wall of the stone trap assembly. Additionally, the impeller reduces accessibility to harvesting mechanisms in the vicinity of the stone trap assembly. This is caused by the fact that when the door is in the opened position, the impeller, which is then in the extended position, blocks access, through the exit and subsequently the entrance of the stone trap assembly, to elements such as the downstream end of the feeder or the inlet of the threshing mechanism. Such access is for example required when servicing these components or when removing or inspecting the cause of a blockage or overload of these mechanisms.
A further stone trap assembly is known from U.S. Pat. No. 5,019,014, which is generally of a similar construction as U.S. Pat. No. 3,576,188. It also comprises an impeller, formed by a longitudinal plate or rake like elements, which in the retracted position are aligned with the back wall of the stone trap assembly. During an evacuation operation a handle can be operated to rotate the impeller 48 together with the door 14 around a hinge pin 34 as shown in the Figure of U.S. Pat. No. 5,019,014 to an extended position (not shown). It is clear that also this stone trap assembly experiences similar problems as described above with reference to US376188.
A further stone trap assembly is known from EP1530895. This stone trap assembly comprises a door which can be moved between an open and an evacuation position, but does not comprise an impeller that is moved together with this door. This stone trap assembly comprises a back wall 76, which, as shown in FIG. 3 of EP1530895 can be removed from its fixed mounting position in order to improve accessibility for servicing elements behind it. The removal of the back wall is a time consuming operation and the lack of an impeller leads to a less efficient evacuation operation of the stone trap assembly.
Still a further stone trap assembly is known from EP2294909, which comprises an elastic wiper that can be deformed to wipe along the transverse back wall of the stone trap assembly when the door moves from closed position to the evacuation position by means of a linear hydraulic actuator. Such a wiper is able to act upon material clogged to this back wall in an attempt to release it, however it does not function as an impeller as the wiper is not able to force the accumulated foreign objects within the stone trap assembly towards the exit of the stone trap assembly. It is further clear that near its mounting point on the back wall the flexible bar of the wiper will not be able to wipe this part near the center of the surface of the back wall, which results in a wiping operation that does not affect any of the material near the center of the stone trap assembly.
Therefor there still exists a need for an improved stone trap assembly which can be operated to allow for a robust and efficient evacuation operation which reduces the risk of compacting or adhering the crop or foreign objects to the stone trap assembly and additionally allows for improved accessibility for inspecting and servicing harvester components via the stone trap assembly.